A report published today by the Office for Standards in Education criticised the guidance given to college teachers.
In the two years since the last major survey of training standards, colleges have made little progress, according to Ofsted.
It said new recruits were often not given enough support by older staff members.
Many college leaders fail to pay adequate attention to teacher training for new staff, even though these trainees are already teaching in their institutions, said the report.
The report focused on the quality of training given to teachers who work in colleges, many of whom specialise in work-related studies.
Miriam Rosen, Ofsted's director of education, said: "Clearly there is still a lot of work that needs to be done. While some improvements have been seen since Ofsted's last survey in 2003, they are not nearly enough.
"Colleges must improve their mentoring schemes and ensure there is systematic support from more experienced teachers.
"These changes, along with improving the practice element of courses, could make a real difference."
Inspectors did not find any trainees whose teaching could be rated as "very good" or "outstanding".
Inspectors said there was a "striking contrast" between the "good" part of the training which was "taught" to the trainees and the "practice" element, which takes place in colleges where trainees are employed as teachers.
Ministers have promised to improve vocational skills in England through a range of new qualifications and centres of excellence.
A spokesman for the Department for Education and Skills said: "We welcome Ofsted's update on the progress that has been made since 2003 and accept that there is still work to be done.
"But implementation of the major initial teacher- training reforms announced in 2004 is progressing well and due to be completed in September 2007.
"We are taking into account Ofsted's findings in 2003 and in this latest report."
The changes being piloted include improved mentoring and more effective observation of teaching practice.
Rosemary Clark, the Association of Colleges' quality manager, said: "Since 2002, it became compulsory for teachers in colleges to have a teaching qualification, and it has been very difficult and costly for colleges to provide mentoring and support for these large numbers of trainees."